1. Field of the Invention
The present invention relates to radiographic image detectors having a scintillator layer with improved flexibility.
2. Description of the Related Art
In a conventional radiographic image detector, an optical coupling layer is disposed between a scintillator panel which converts radiations into light, and a photoelectric conversion element to prevent the scattering of light. Materials such as pressure sensitive adhesives, liquid resin adhesives and optical oils are used as the optical coupling layers. However, the use of these materials in the bonding of a scintillator panel and a photoelectric conversion element encounters problems described below. In the case of pressure sensitive adhesives, a gap is caused due to the thickness distribution in the scintillator layer or the irregularities present on the photoelectric conversion element, resulting in the occurrence of a bonding failure and consequent problems such as separation charging and image defects. In the case of liquid resin adhesives and optical oils, the thickness of the resin or the oil becomes nonuniform due to the thickness distribution in the scintillator layer or the irregularities on the photoelectric conversion element, resulting in a failure to achieve in-plane uniformity of image quality. In particular, these problems are more pronounced when the scintillator layer has a large thickness distribution or when a plurality of photoelectric conversion element panels are combined.
To solve the aforementioned problems, a polymer film is used as a substrate for a scintillator layer (see, for example, Patent Literature 1). Because polymer films have flexibility, the use of a polymer film as a substrate makes it possible that the substrate and the scintillator layer can be deformed in conformity with the shape of the light-receiving surface of a light-receiving element. According to Patent Literature 1, the distance between a scintillator layer and a light-receiving surface is rendered uniform by causing the deformation of the substrate and the scintillator layer constituting a radiation flat panel detector, thereby improving the resolution associated with radiation detection.
In this radiation flat panel detector, however, the scintillator layer which is poor in flexibility can incur problems such as separation or crystal breakage in the case where the scintillator layer has large thickness distribution or significant geometric changes on the side adjacent to the light-receiving surface.
To solve the above problems, a columnar crystal scintillator layer is formed on a flexible substrate and a moistureproof protective layer (polyparaxylylene) is formed to cover the scintillator layer and to fill between the columnar crystals, thereby preventing the breakage of the crystals (see, for example, Patent Literature 2).
However, the placement of a moistureproof protective layer between the columnar crystals does not improve the flexibility of the scintillator layer itself and thus is not a fundamental solution.